1. Technical Field
The disclosure relates to radio-frequency identification tag devices, and in particular, to radio-frequency identification (RFID) tag antennas, tags and communications systems using the same.
2. Description of the Related Art
Radio-frequency identification (RFID) systems have been applied in many fields such as in supply chain management, security, tracking and other commercial applications. Thus, RFID innovative developments have been driven by users wanting to improve upon the technology, such as in the supply chain management process. The RFID systems allow transparency throughout the distribution chain including manufacturers, suppliers, distributors and retailers, providing information such as product type, location, date, etc. One of the greatest benefit of RFID systems is to improve upon supply chain management efficiency, as an example. At present, most product information is recorded in barcodes, and the information is then retrieved by scanning the barcode using a scanner. Meanwhile, the RFID tag antennas can be detected within a certain range, and a large amount of information can be processed simultaneously.
However, the shortcomings of the design and application of conventional RFID tag antennas are that the fabrication costs thereof are expensive. At present, costs for RFID tag antennas take the largest proportion among costs of RFID devices. Recently, process improvements have been made to lower fabrication costs of the RFID tag antenna. For example, RFID tag antenna conductors can be made of silver paste using the roll-to-roll manufacturing process or screen printing process or other printing methods to reduce fabrication costs. In the fabricating process however, the amount of silver paste required is a key portion of the total fabrication material cost of the RFID tag antenna.
U.S. Pat. No. 7,277,017, the entirety of which is hereby incorporated by reference, discloses an RFID tag antenna, implemented by a dipole antenna (dipole) tag antenna or a Central Loop (loop) consisting of a conductor.
FIG. 1 is a schematic plan view illustrating a conventional RFID tag antenna. Referring to FIG. 1, in the conventional RFID tag antenna 10, an antenna pattern 12 is formed on the substrate 11. An IC chip 13 is disposed on the antenna pattern 12. The antenna pattern 12 can serve as a dipole antenna which includes two singular pole patterns 121 and 122. Each of the two singular pole patterns 121 and 122 extends outwardly from the position of the IC chip 13. The antenna pattern 12 further includes a correction loop 123 to compensate or adapt to antenna characteristics. The correction loop 123 bypasses the position of the IC chip 13 and connects to the two singular pole patterns 121 and 122.
FIG. 2 is a schematic plan view illustrating another conventional RFID tag antenna. Referring to FIG. 2, in the conventional RFID tag antenna 10, an antenna pattern 12 is formed on the substrate 11. An IC chip 13 is disposed on the antenna pattern 12 which includes a loop antenna. Two extension portions 12a and 12b extend outwardly from the position of the IC chip 13. The two extension portions 12a and 12b are respectively connected to the IC chip 13 and a correction loop 123. The IC chip 13 is further connected to a conductive pattern 16. Both sides of the correction loop 123 respectively include dual patterns 123a and 123b which purpose to remove the parasitic capacitance between the IC chip 13 and the antenna pattern 12.
However, the inductance generated by the loop antenna does not effectively eliminate the capacitance generated between the conductor and the IC chip. Furthermore, controlling RFID tag antenna resonance frequencies for conventional RFID tag antennas is difficult.